Could Iridium flashes cause eye damage?

Robert Sheaffer (
Mon, 15 Dec 1997 08:07:56 -0800 (PST)

Joe Dellinger
> 	At the local astronomy club meeting I gave a short presentation on
> the Iridium flashes, to see if anyone else was interested in observing one.
> One fellow with a whopper telescope (20-inch diameter) wanted to know what
> would happen if he were unlucky enough to be looking at something at the spot
> in the sky just where the satellite happened to flash. Certainly it would be
> dazzling.Could it conceivably cause eye damage? If not in that size telescope,
> what about in an even larger one?

No. No celestial object other than the sun has ever resulted in 'eye damage'
for anyone looking at it in a telescope.

> 	My first answer was "of course not", but then he told me that even in
> his size scope it is dangerous to look at the moon without a filter. To back
> this up he pointed out that he can make a piece of paper start smoking by
> holding it at prime focus while his scope is pointed at the full moon.

Your friend is a spinner of tall tales. Bet him $100 that he *can't* do this.
I guarantee that he will back down.

> 	Hmmm. You can't make an extended source of light any brighter by
> magnifying it. However, if the satellite makes a perfect mirror, then at SOME
>(implausibly high?) level of magnification all you will see is the mirror-image
> of the sun, and thus looking at the satellite should become, if for only an
> instant, approximately equivalent to looking at the sun. That is certainly not
> something you want to do.

No, because the solar energy falling on the Iridium's antenna/mirror is
diluted to the size of the solar disk projected on the earth, many
kilometers across. Hence it is much more dilute than a direct peek
at the solar disk.

        Robert Sheaffer - - Skeptical to the Max!

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